In the Bible we see a prophet is like the mouth of God (Ex. 4:16; Ex. 7:1 - Aaron was called Moses' prophet for he was his speaker). They did not claim their message was theirs. They prefaced their message with, "Thus saith the Lord", and they foretold much about the future. Prophets were an integral part of revealing God's will. Yet God knew that some would rise up claiming to be a prophet when in fact they were not. He knew that if He was to give His divine will to some, others would claim to have it too. Thus God devised a way to know who was a prophet and who was not.
Deuteronomy 18:20-22 says when one supposes to speak for the Lord, if the thing does not happen or come to pass then the Lord has not spoken. Galatians 1:6-9 adds that when anyone (including an angel or apostle) speaks a different gospel then a curse rests upon him. These two passages say we can test the predictions made by supposed prophets and their words if in anyway they contradict what is already revealed (the Bible).
Joseph smith fails the test of a prophet because...
His predictions failed. In Doctrine and Covenants, section 84, Joseph Smith prophesied that New Jerusalem and a Mormon temple was to be built in Zion, Missouri by his generation and that he would dedicate it with his own hand. Yet Mormons were run out of Missouri and a temple was never built during Smiths' life nor by his contemporary generation.
In Doctrine and Covenants, section 111, Joseph Smith prophesied that Salem, Massachusetts would be given to the Mormons and in it they would find great treasure to pay all their debts. The Mormons never received Salem nor any treasure.
His book is full of errors. He writes of horses, oxen, and cows as native to North America (1 Nephi 18:25). Yet, these animals were all introduced by European settlers.
He has Jesus saying, "I am the alpha and omega" in the book of Mormon. Those are Greek terms, but the book of Mormon supposedly came to the Native American Indians who would not have known Greek. It looks like Joseph Smith did a little borrowing from the Bible and a little lying about the Indians.
His book is full of changes. I have in my possession a book entitled "The 3,913 changes made to the Book of Mormon". If Joseph Smith truly was a prophet from God why would there need to be any changes? God's word does not change. There have been no changes to the Bible. Mormons claim their book is the most accurate translation, yet as time goes on they keep "updating" their book.
The gift of prophesy ended long before Joseph Smith. Joseph Smith lived in the 1800's yet the Bible tells us that when God's word was complete, prophesy would end (1 Cor. 13:8). The word of God came to completion at the end of the 1st century. Jude wrote of "the faith which was once for all delivered to the saints." And when John laid down his pen he closed the scriptures with a warning not to add to it nor take from it (Rev. 22:18-19). Yet we are told to believe that nearly 1700 years later a man came along and added more to it! Joseph Smith fails the test of a prophet and passes the test of a false prophet (Matt. 7:15-20).
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